Don't add warnings filter on import

The changeset module was adding a warnings filter on import. This
affects all applications that wind up importing it. A library
shouldn't modify the warnings filters unless asked.

Closes-Bug: #1407736
Change-Id: I893f8be48efd3d3642e977ab587c9e6dc867258b

migrate/changeset/__init__.py

@@ -5,13 +5,10 @@
    .. [#] SQL Data Definition Language
 """
 import re
-import warnings
 
 import sqlalchemy
 from sqlalchemy import __version__ as _sa_version
 
-warnings.simplefilter('always', DeprecationWarning)
-
 _sa_version = tuple(int(re.match("\d+", x).group(0)) for x in _sa_version.split("."))
 SQLA_07 = _sa_version >= (0, 7)
 SQLA_08 = _sa_version >= (0, 8)

migrate/tests/versioning/test_shell.py

@@ -485,7 +485,6 @@ class TestShellDatabase(Shell, DB):
         result = self.env.run('migrate compare_model_to_db %s %s --model=%s' \
             % (self.url, repos_path, model_module.replace(":", ".")), expect_error=True)
         self.assertEqual(result.returncode, 0)
-        self.assertTrue("DeprecationWarning" in result.stderr)
         self.assertTrue("tables missing from database: tmp_account_rundiffs" in result.stdout)
 
         # Update db to latest model.